Income Taxes - Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Unrecognized Tax Benefits [Roll Forward]
Beginning balance	$ 2,053	$ 2,158	$ 2,485
Additions for tax positions related to the current year	62	39	59
Additions for tax positions of prior years	21	53	89
Reductions for tax positions of prior years	(62)	(35)	(23)
Settlements with taxing authorities	(65)	(35)	(6)
Statute closings and audit resolutions	(82)	(127)	(446)
Ending balance	$ 1,927	$ 2,053	$ 2,158

Unrecognized Tax Benefits, Reduction Resulting From Lapse Of Applicable Statute Of Limitations And Audit Resolutions

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount of unrecognized tax benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 217
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482663/740-10-55-217

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 15A
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-15A

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 10B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482525/740-10-45-10B

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- Definition

Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

+ References

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- Definition

Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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- Definition

Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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- Definition

Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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